In recent years, for THz wave band (0.1 THz to 10 THz) positioned in intermediate frequencies between electromagnetic waves and light waves, studies of applicabilities of ultra high-speed wireless communications, sensing, imaging, etc. have become active, and there has been expected its practical application. However, since THz-wave systems are composed of large-sized and three-dimensional structured components under the current circumstances, large-sized and expensive configurations are required for such THz-wave systems. In order to miniaturize the whole of such systems, implementation of THz-wave ICs integrating devices is indispensable.
Utilization of technologies of both of a light wave region and an electric wave region can be considered as fundamental technologies of the THz-wave ICs. However, optical components, e.g. lenses, mirrors, are composed of large-sized and three-dimensional structured components, and therefore are not suitable for the integration. Moreover, it is becoming difficult to produce hollow metal waveguides used in the electric wave region due to its fine three-dimensional structure. A waveguide loss in planar metallic-transmission lines is increased as effect of metallic absorption is increased.
As a fundamental technology of THz-wave ICs, there has been studied applicability of a 2D-PC slab where outstanding progress is seen in the light wave region (e.g., refer to Non Patent Literatures 1-3.).
The waveguide for the THz wave band is standardized in a range from WR6 (110 GHz to 170 GHz) to WR1 (0.75 THz to 1.1 THz). Although the cross-sectional size is as small as in a range from 1651 μm×826 μm to 254 μm×127 μm, it needs to be formed by machining and be fixed with a screw at the connection. For example, there is a loss of approximately 0.5 dB in WR3 (220 GHz to 325 GHz) (e.g., refer to Non Patent Literature 4.).
Moreover, there have been also reviewed resonant and waveguiding line defect modes in a two-dimensional electromagnetic band-gap slab structure for millimeter wave frequency bands (e.g., refer to Non Patent Literature 5.).
Moreover, generally in the PC waveguide, since not only the THz wave band, but also a terminal portion of the waveguide has a large refractive index difference between semiconductor and air, there is influence of light interference (Fabry-Pérot resonance) and multiple reflection due to edge face reflection (e.g., refer to Non Patent Literature 6.).